A Kuala Lumpur Fire and Rescue Department spokesman at the scene of the incident said a 19-metre stretch of the route along Jalan Imbi sank in the incident at 10.30am.
Fortunately, he said, no loss of life was reported.
"A preliminary report found it could have been caused by a burst Syabas main pipe but investigation is still going on, he said.
In a follow up to the incident, the KL Monorail Service from Hang Tuah Station was stopped due to the underground soil collapse near the monorail pillar at the intersection.
Kuala Lumpur Fire and Rescue department assistant director (operations) Azizan Ismail said the tunnel, which is part of Pudu underpass project by Kuala Lumpur City Hall (DBKL), sunk twice at approximately 10.38am and 12.20pm.
"We predict that the road will collapse further along the tunnel line.
It was learnt that two idle excavators were in the tunnel when the incident occurred but no casualties have been reported," he said.
The Mass Rapid Transit Corporation Sdn Bhd (MRT Corp) denied that the road collapse was connected with the MRT project.
"MRT Corp wishes to state unequivocally the alignment of the MRT Sungai Buloh-Kajang Line does not pass that location," it said in a statement.